Conventionally, a nuclear magnetic resonance apparatus has been known which comprises a nuclear magnetic resonance means for elucidating an atom configuration and a molecular structure of a substance based on a decay signal of induced electromotive force caused by resonance precession of nuclear magnetic moment induced by irradiation of electro-magnetic pulses in an RF region when a substance is exposed to a strong magnetic field, and a vibration isolation mechanism for suppressing vibration of this nuclear magnetic resonance means (see e.g., Japanese Patent Laid-Open publication No. 2001-145611, paragraph [0011], FIG. 1).
A vibration isolation mechanism itself of an active type using an air spring has also been known (see, e.g., “6DOF microvibration Control System using Air Actuators (Experimental Study on Vibration Isolation and Damping Performance)”, Yasutaka TAGAWA and four others, Proceedings of Dynamics and Design Conference'94, JSME, No. 940-26(II), pp. 544, 1994.07).
In a vibration isolation mechanism constituted by a spring-mass system (a surface plate and a mounted component), i.e. a vibration isolation mechanism of the passive type, vibration is amplified by resonance at a natural frequency of the spring-mass system. In contrast to this, the vibration isolation mechanism of the active type is a vibration isolation mechanism comprising a means for detecting a vibration state or a displacement state of a component to be isolated from vibration, namely, a controlled object, a control means for outputting a signal to cancel the vibration of the controlled object based on a detected signal by the detection means, an actuator (e.g., air spring, piezoelectric laminate) for exerting a force on the controlled object to cancel the vibration by receiving a signal from the control means, and the like, whereby feedback control is performed to avoid the resonance at the natural frequency and to suppress the amplification of the vibration by the resonance. This active type vibration isolation mechanism has become indispensable particularly for precision mechanical equipment adversely affected easily even by micro-vibration.
In the case of the apparatus described in the Japanese Patent Laid-Open publication No. 2001-145611 in which a passive-type vibration isolation mechanism is employed as the vibration isolation mechanism, since a vibration is amplified at around the natural frequency as described above, the vibration isolation mechanism is unsuitable for vibration isolation of a nuclear magnetic resonance apparatus which is a precision measuring instrument. That is, in the case of the nuclear magnetic resonance apparatus using the passive type vibration mechanism, since the vibration of the apparatus causes side band noise in a nuclear magnetic spectrum responsive to a frequency of the vibration, such a problem arises that precision measurement can not be performed by the apparatus.
On the other hand, the aforementioned active type vibration isolation mechanism employs such a constituent element as a servo valve or a servo acceleration sensor which may lead to malfunctions or operating failures under the influence of an external strong magnetic field. Therefore, even if a nuclear magnetic resonance apparatus formed by applying this active type vibration isolation mechanism of the conventional type to the nuclear magnetic resonance means which is a source of a strong magnetic field, such a problem arises that the vibration isolation mechanism does not operate normally, with the result that it becomes impossible to perform precision measurement also by this nuclear magnetic resonance apparatus as in the foregoing case.
It is an object of the present invention to provide a nuclear magnetic resonance apparatus which solves the above-described problems of the prior art and which allows the vibration isolation mechanism to fully exert an inherent performance even under a strong magnetic field, thereby suppressing vibration and enabling precision measurement.